1. Field of the Invention
The present invention relates to a liquid crystal display apparatus provided with a support spacer for holding a cell gap for a liquid crystal layer.
2. Description of the Related Art
Various kinds of liquid crystal display apparatuses using thin-film transistors (TFTs) are known in accordance with forms. For one of the forms, a liquid crystal display apparatus using an inverted stagger type thin-film transistor is exemplified. The liquid crystal display apparatus will be described referring to the liquid crystal display apparatus using the inverted stagger type thin-film transistor.
When the cell gap for a liquid crystal layer is formed between transparent substrates, spacers are used. By the spacers, the uniformity of the cell gap can be improved in the liquid crystal display apparatus with the large size substrates.
FIG. 1 shows a concept of the spacer in a conventional example of the liquid crystal display apparatus. In FIG. 1, support spacers 500c and 500d are used. The supporting spacers 500c and 500d are located in regions corresponding to light shielding layers (black matrix) 12. A color filter (color layer) 13 is arranged between the light shielding layers 12 in a lateral direction. A transparent substrate 14 is located above the color filter 13 and the light shielding layers 12.
FIG. 2 is a schematic cross sectional view of an in-phase switching type liquid crystal display apparatus in a first conventional example. A display cell 501 is composed of a polarizing plate 17 and an electric conducting layer 16 formed on the front surface of a transparent substrate 14, a color filter 13 and flattening films or light shielding layers 12 formed on the back surface of the transparent substrate 14 and the supporting spacers 500c and 500d extending from the light shielding layers 12. The display cell 501 is composed of a passivation film 22, an interlayer insulating film 10, a gate electrode 3 and a common electrode 4 formed on the front surface of a transparent substrate 9, and a polarizing plate 18 formed on the back surface of the transparent substrate 9. The supporting spacers 500c and 500d are adhered to the light shielding layers 12 and the passivation film 22. The adhesion of the supporting spacer to the light shielding layer 12 on the side of the transparent substrate 14 is higher than that of the supporting spacer to the passivation film 22 on the side of the transparent substrate 9. Consequently, when an external pressure is applied to the display cell 501, the supporting spacers 500c and 500d are moved from specified positions on the side of the passivation film 22 because of the external pressure. The movement of the supporting spacers 500c and 500d induces color irregularity.
FIG. 3 is a plan view of the display cell of a second conventional example of the in-phase switching type liquid crystal display apparatus. A display cell 502 is composed of an amorphous silicon film 1, a pixel electrode 2, a gate electrode 3, a common electrode 4, data line 5, source electrode 6, a drain electrode 7, and a supporting spacer 500. FIG. 4 is a cross sectional view of the display cell 502 in a region of the supporting spacer 500 along the line X-Xxe2x80x2 of FIG. 3. In FIG. 4, the upper substrate section of the display cell is composed of a polarizing plate 17 and an electric conducting layer 16 formed on the front surface of a transparent substrate 14, and a black matrix layer 12, a color layer (color filter) 13, a flattening film 15, and an orientation film 11 formed on the back surface of the transparent substrate 14. A part of the flattening film 15 functions as the supporting spacer 500. The surface of the supporting spacer 500 is covered by the orientation film 11. In FIG. 4, the lower substrate section of the display cell 500 is composed of an orientation film 11, a passivation film 22, an interlayer insulating film 10 and a gate electrode 3 formed on the front surface of a transparent substrate 9, and a polarizing plate 18 formed on the back surface of the transparent substrate 9. A liquid crystal layer 20 is formed in the cell gap supported by the supporting spacer 500. The supporting spacer 500 has the low adhesion on the side of the lower substrate section of the display cell 500. Accordingly, when the display cell is pressed, the supporting spacer 500 may be moved. If the supporting spacer 500 moves, color irregularity is caused.
FIG. 5 is a plan view of a display cell in a third conventional example of an in-phase switching type liquid crystal display apparatus. A display cell 503 is composed of an amorphous silicon film 1, a pixel electrode 2, a gate electrode 3, a common electrode 4, a data line 5, a source electrode 6, a drain electrode 7, and a supporting spacer 500. In the display cell 503, the supporting spacer 500 is arranged on the gate electrode 1. FIG. 6 is a cross sectional view of the display cell 503 in a region of the supporting spacer 500 along the line Y-Yxe2x80x2 in FIG. 5. In FIG. 6, the upper substrate section of the display cell is composed of a polarizing plate 17 and an electric conducting layer 16 formed on the front surface of a transparent substrate 14, and a black matrix layer 12, a color layer (color filter) 13, a flattening film 15, and an orientation film 11 formed on the back surface of the transparent substrate 14. A part of the flattening film 15 functions as the supporting spacer 500. On the other hand, the lower substrate section of the display cell 503 is composed of the orientation film 11, a passivation film 22, an interlayer insulating film 10 and a gate electrode 3 formed on the front surface of a transparent substrate 9, and a polarizing plate 18 formed on the back surface of the transparent substrate 9. The passivation film 22 is formed to have a concave section. The supporting spacer 500 is loaded in the concave section. The liquid crystal layer 20 is formed in the cell gap formed by the supporting spacer 500.
Because the supporting spacer 500 is loaded on the concave section, the resistance against the movement in the lateral direction is higher than in the supporting spacer shown in FIGS. 3 and 4. However, since the depth of the concave section is extremely shallow, the improvement of the strength of a great extent cannot be expected. Consequently, when the display cell is externally pressed, the supporting spacer 500 may be moved. If the supporting spacer 500 moves, color irregularities result.
FIG. 7 shows a plan view of the display cell of a fourth conventional example of the in-phase switching type liquid crystal display apparatus. The display cell 504 is composed of an amorphous silicon film 1, a pixel electrode 2, a gate electrode 3, a common electrode 4, a data line 5, a source electrode 6, a drain electrode 7, and supporting spacers 500a and 500b. In the display cell 504, the supporting spacers 500a and 500b are located on the data lines 5. FIG. 8 is a cross sectional view of the display cell 504 in the region of the supporting spacers 500a and 500b along the line Z-Zxe2x80x2 in FIG. 7. In FIG. 8, the upper substrate section of the display cell 504 is composed of a polarizing plate 17, an electric conducting layer 16 formed on the front surface of a transparent substrate 14, and a black matrix layer 12, a color layer (color filter) 13, a flattening film 15, and an orientation film 11 formed on the back surface of the transparent substrate 14. A part of the flattening film 15 is formed to have the supporting spacers 500a and 500b. In FIG. 8, the lower substrate section of the display cell 504 is composed of an orientation film 11, s passivation film 22, data lines 5 and 5xe2x80x2, pixel electrodes 2, an interlayer insulating film 10, and common electrodes 4 formed on the front surface of a transparent substrate 9, and a polarizing plate 18 formed on the back surface of the transparent substrate 9.
The liquid crystal layer 20 is provided in the cell gap supported by supporting spacers 500a and 500b. The supporting spacers 500a and 500b provides the low adhesion on the side of the transparent substrate 9 as in the case of the supporting spacer 500 shown in FIGS. 3 and 4. When the display cell is externally pressed, the supporting spacers 500a and 500b be moved. If the supporting spacers 500a and 500b are moved, color irregularities result.
In the conjunction with the above description, a liquid crystal display is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 6-175156). In this reference, the liquid crystal display is composed of a substrate on which a thin film transistor is formed to drive liquid crystal and a substrate on which a transparent electrode is formed. A liquid crystal layer is formed between the substrates. A black matrix layer is formed on the substrate on which the above-mentioned thin film transistor is formed. A source wiring of the above-mentioned thin film transistor is used for the black matrix layer. A light shielding section is formed in an island manner to overlap the matrix layer through a gate wiring of the thin film transistor of a previous stage and an insulating film. Also, the light shielding section is electrically connected with a drain electrode through the insulating film.
Also, a liquid crystal display apparatus is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 10-96955). In this reference, the liquid crystal display apparatus is composed of a first substrate in which a plurality of address wiring lines, a plurality of data wiring lines and a plurality of switching elements are formed on an insulation substrate, a pixel electrode 2 is formed on the switching element via an insulating film, and an auxiliary capacity section is electrically connected to the pixel electrode 2. The liquid crystal display apparatus is further composed of a second substrate in which a counter electrode is formed on an insulation substrate, and a liquid crystal layer between the first and second substrates. The auxiliary capacity electrode is composed of an auxiliary capacity electrode formed in the same layer as the data wiring line, an auxiliary capacity electrode located on the counter side to the an auxiliary capacity electrode via an insulating film. A column spacer is accommodated in a contact hole for a contact between the auxiliary capacity electrode and the pixel electrode to keep a gap from the second substrate.
Also, a liquid crystal display apparatus is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 10-228023). In this reference, the liquid crystal display apparatus is composed of a liquid crystal layer between substrates with electrodes. The liquid crystal display apparatus is further composed of an orientation control layer, an organic material layer which has a shape memory characteristic, and a spacer which is formed to have a wall or column shape on the orientation control layer. A rubbing process to the orientation control layer is carried out after the formation of the spacer, and a heating process to a glass transition point or above is carried out after the rubbing process.
Therefore, an object of the present invention is to provide a liquid crystal display apparatus in which the strength of a supporting spacer can be improved.
Another object of the present invention is to provide a liquid crystal display apparatus in which a cell gap can be uniformly kept so that display irregularities can be made less.
In an aspect of the present invention, a liquid crystal display apparatus using a thin film transistor, includes first and second substrate sections and a liquid crystal layer provided between the first substrate section and the second substrate section. A supporting spacer extends from the first substrate section. The second substrate section has a concave section. The tip portion of the supporting spacer engages the concave section to keep a gap from the first substrate section.
Here, the supporting spacer may have an extending portion in the tip portion in a direction orthogonal to a direction to which the supporting spacer extends.
Also, the supporting spacer may be covered by an orientation film, and the concave section may be covered by an orientation film.
Also, when the thin film transistor has a gate electrode, a source electrode connected to a pixel electrode and a drain electrode connected to a data line extending in a direction orthogonal to a direction of the gate electrode, the supporting spacer and the concave section may be provided above the gate electrode. In this case, one of the first and second substrate sections desirably includes the pixel electrode and a common electrode provide to drive liquid crystal molecules together with the pixel electrode. Alternatively, one of the first and second substrate sections may include the pixel electrode, and the other of the first and second substrate sections may include a common electrode provided to drive liquid crystal molecules together with the pixel electrode.
Also, when the thin film transistor has a gate electrode, a source electrode connected to a pixel electrode and a drain electrode connected to a data line extending in a direction orthogonal to a direction of the gate electrode, the supporting spacer and the concave section may be provided above the data line. In this case, one of the first and second substrate sections may include the pixel electrode, and a common electrode provide to drive liquid crystal molecules together with the pixel electrode. Alternatively, one of the first and second substrate sections may include the pixel electrode, and the other of the first and second substrate sections may include a common electrode provided to drive liquid crystal molecules together with the pixel electrode.
Also, the supporting spacer may be formed of organic material or inorganic material.
Also, the first substrate section may include a first transparent substrate, a light shielding layer formed in a region other than a pixel region on an opposing surface of the first transparent substrate to the second substrate section, and a flattening film formed to cover the light shielding layer. At this time, the supporting spacer is desirably formed in a region where the light shielding layer is formed. In this case, the supporting spacer may be formed from a part of the flattening film. Also, the flattening film is desirably formed of transparent material.
Also, the supporting spacer may be adhered to the first substrate section. In this case, the first substrate section may have another concave section with which the supporting spacer engages, and the supporting spacer is adhered to the other concave section. In this case, the supporting spacer may be formed of metal or organic material.